Two-part restriction element for large-bore downhole isolation tool and method

1. A downhole isolation system for sealing a well with a large-bore plug, the downhole isolation system comprising:

a setting tool having an internal chamber defined by a reactionary sleeve and a mandrel of the setting tool;

a first restriction element entirely placed within the internal chamber of the setting tool; and

a second restriction element entirely placed within the internal chamber, separate from the first restriction element,

wherein the first restriction element includes a passage that extends throughout the first restriction element, and

wherein the second restriction element fits inside a first part of the passage.

2. The system of claim 1 , wherein an external diameter of the first restriction element is larger than an external diameter of the second restriction element.

3. The system of claim 1 , wherein the passage has the first part and a second part, the second part having a smaller diameter than the first part, and the second restriction element fits inside the first part, but not the second part.

4. The system of claim 1 , wherein the first restriction element comprises a flexible element located inside the passage and configured to allow the second restriction element to move one way only along the passage.

5. The system of claim 1 , further comprising: a biasing mechanism that exerts a force on the first restriction element.

6. The system of claim 1 , further comprising:

a large-bore plug attached to the setting tool.

7. The system of claim 1 , wherein the mandrel of the setting tool extends through a passage formed throughout the first restriction element and connects to the large-bore plug.

8. The system of claim 7 , wherein the second restriction element is placed between the mandrel and the reactionary sleeve.

9. A downhole isolation system for sealing a well, the downhole isolation system comprising:

a large-bore plug having a seat at an upstream end, wherein the large-bore plug does not include a mandrel so that a diameter of an inner bore of the large-bore plug is not limited by the mandrel;

a first restriction element configured to sit in the seat of the large-bore plug; and

a second restriction element configured to fit inside the first restriction element,

wherein the first restriction element includes a passage that extends throughout the first restriction element, and

wherein the second restriction element fits inside a first part of the passage.

10. The system of claim 9 , wherein an external diameter of the first restriction element is larger than an external diameter of the second restriction element.

11. The system of claim 9 , wherein the passage has the first part and a second part, the second part having a smaller diameter than the first part, and the second restriction element fits inside the first part, but not the second part.

12. The system of claim 9 , wherein the first restriction element comprises a flexible element located inside the passage and configured to allow the second restriction element to move one way only along the passage.

13. The system of claim 9 , further comprising:

a setting tool having an internal chamber,

wherein the first and second restriction elements fit inside the internal chamber.

14. The system of claim 13 , wherein the setting tool further comprises: a biasing mechanism that exerts a force on the first restriction element.

15. The system of claim 13 , wherein the setting tool includes a mandrel and a reactionary sleeve that define the internal chamber.

16. The system of claim 15 , wherein the mandrel of the setting tool extends through a passage formed throughout the first restriction element and connects to the large-bore plug.

17. The system of claim 16 , wherein the second restriction element is placed between the mandrel and the reactionary sleeve.

18. A method for plugging a well with a large-bore plug, the method comprising:

releasing a first restriction element from within an internal chamber of a setting tool;

releasing a second restriction element from within the internal chamber;

seating the first restriction element in a corresponding seat of the large-bore plug,

wherein the large-bore plug does not include a mandrel so that a diameter of an inner bore of the large-bore plug is not limited by the mandrel; and

seating the second restriction element within the first restriction element,

wherein the first restriction element includes a passage that extends throughout the first restriction element, and

wherein the second restriction element fits inside a first part of the passage.

19. The method of claim 18 , further comprising:

setting up the large-bore plug with the setting plug, before seating the first and second restriction elements.

20. The method of claim 18 , further comprising:

placing a mandrel of the setting tool through a passage of the first restriction element.

21. The method of claim 20 , further comprising:

placing the second restriction element inside the setting tool, between the mandrel and a reactionary sleeve.

22. The method of claim 21 , further comprising:

placing the mandrel through the large-bore plug.

23. The method of claim 22 , further comprising:

activating the setting tool to set up the large-bore plug.

24. The method of claim 23 , further comprising:

pulling the setting tool apart from the large-bore plug.

25. The method of claim 24 , further comprising:

increasing a pressure inside the well to seat the first and second restriction elements.

26. The method of claim 18 , further comprising:

flowing back the well to remove the first restriction element from the large-bore plug, wherein the second restriction element is trapped inside a passage of the first restriction element.

27. The method of claim 26 , further comprising:

trapping the first and second restriction elements inside the setting tool; and

retrieving the setting tool and the first and second restriction elements to the surface.